The present invention relates to nuclear magnetic resonance (NMR) imaging and, more particularly, to a novel method of three-dimensional NMR flow-contrast angiographic imaging having a high degree of suppression of stationary material.
Non-invasive NMR imaging techniques can be utilized to detect flowing fluids, such as blood, in a sample, such as the human body, being analyzed. Techniques such as NMR angiography provide a selective means of fluid flow detection in blood vessels and the like, although the results do not always correlate well with other techniques, such as X-ray angiography, in measuring projected vessel anatomy, such as might be clinical useful in detecting atherosclerotic plaque. This lack of correlation appears to be due to the limited NMR image resolution caused by an inherently low signal-to-noise ratio, and flow effects which frequently cause artifactual loss of signal intensity. Thus, present NMR flow imaging techniques, and particularly those techniques based upon phase effects, can provide important flow information, but only limited morphological information. Typical of the morphological information desired is the angiographic projection imaging of the bifurcations of the carotid arteries, which bifurcations are a frequent site of atheromatous plaque formation, which is itself a precursor of transient ischemic attack and stroke. It is therefore highly desirable to be able to image atherosclerotic plaque (especially prior to the ulcerization thereof, which may result in subintimal hemorrhage or brain emboli therefrom). The presence of smooth atherosclerotic plaque, causing hemodynamically significant stenosis, is presently clinically evaluated with a standard X-ray dye angiographic procedure, in which clinical evaluation of carotid artery disease requires injection of a contrast dye, via a catheter, in an invasive test which is not totally benign. It is therefore highly desirable to use a non-invasive magnetic resonance technique which provides a display in which only the arterial blood flow appears, with the stationary surrounding tissue and the blood flow in the adjacent veins being effectively suppressed.